The invention generally relates to digital image capturing and more particularly to an image capturing apparatus using low-resolution sensors and optical spatial image sampling techniques.
High resolution digital image capturing systems such as high-end digital camera 100 shown in FIG. 1A typically utilize Charge Couple Device (CCD) array 101, which consists of thousands of photo-sensitive cells, to sample the image and produce varying amounts of electrical charges in response to the amount of light received from the image subject via an optical lens (not shown). The collected electrical charges are then converted into digital bits representing the image using external Analog-to-Digital (ADC) converter 102. The digital bits are then provided to multiplexer 103 which selectively transfers them to Digital Signal Processor (DSP) 104 before being stored in a memory. Central Processing Unit (CPU) 105 is also normally required for general processing (e.g., data formatting, etc.), power management, data transfer, and other tasks. A typical CCD sensor array is capable of capturing very high-resolution images. However, a CCD array requires a specialized manufacturing process, other than standard Complementary Metal-Oxide-Semiconductor (CMOS) manufacturing process, and is therefore expensive. Additionally, having the CCD array separate from the ADC means that different manufacturing processes are required for the CCD array and the external ADC which drives up the cost. The external ADC also needs board layout restraints for optimal operation thereby further increasing the cost. In addition, a high performance specialized DSP is necessary to complement the CCD array which further increases the cost. As a result, in general, high-resolution digital cameras are very expensive. Additionally, a CCD array with its control circuit tends to have high power consumption.
Recently introduced high-resolution digital cameras such as that shown in FIG. 1B utilize CMOS sensor imagers wherein a CMOS-based array of sensors 121 is integrated with ADC 122 and multiplexer 123 on the same silicon substrate. In so doing, the more expensive CCD array is replaced by the less expensive CMOS sensor array. Moreover, separate manufacturing processes for the sensor array and ADC are no longer needed which tend to decrease the manufacturing cost. However, a high performance specialized DSP is still required to complement the CCD array which means that these high-resolution digital cameras are still rather expensive.
On the other hand, low-resolution digital cameras such as that shown in FIG. 1C utilize a CMOS-based array of pixel-level sensors 131 wherein CMOS sensor array 131 is integrated with digital interface circuit 132 coupled to CPU 133 via a system bus. Each of these pixel-level sensors integrates a photo-diode, an ADC, and a latch together and is capable of capturing fairly low-resolution images. Such a CMOS array of pixel level sensors is very inexpensive as well as consumes less power than its CMOS-based image sensor array counterpart discussed above. Moreover, separate manufacturing processes are not required for the sensor array and the digital interface circuit thereby reducing the associated manufacturing costs. As a result, such digital cameras are very inexpensive but are capable of only capturing and generating low-resolution images. Hence, there is a need for a high-resolution digital image capturing apparatus that is inexpensive.
U.S. Pat. No. 5,612,736 (hereinafter the ""736 patent) teaches a digital camera wherein light from a subject is directed by camera lens to a Digital Micro mirror Device (DMD) array which consists of a plurality of mirrors. Each of these mirrors represents a single pixel of the subject image. These mirrors can be energized by a DMD driver according to a serial sequence wherein each mirror is physically rotated to direct the light from the pixel associated with the corresponding mirror to a detector or a light absorber, respectively, thereby switching between an ON position and an OFF position. A complete sequential scan of the pixel mirrors in the DMD array provides complete digital information as to the color and intensity of the image subject pixels. The sequencing digital information is then provided to an Analog-to-Digital converter (ADC) before being stored in memory which can subsequently be retrieved to generate a digital image. The digital camera of patent ""736 captures the digital information of the image one pixel at a time which leads to only a serial stream of data which will need to be processed before the image is obtained. Moreover, because of the fixed number of pixel mirrors and the pixel mirrors can only be switched between an ON and an OFF position, the resolution of the images are therefore fixed. Furthermore, the digital camera of the ""736 patent requires an array of mirrors which are expensive. The digital camera size is also controlled by the level of miniaturization of these mirrors which may greatly affect the cost.
U.S. Pat. No. 5,212,555 (hereinafter the ""555 patent) teaches a digital camera utilizing a Spatial Light Modulator (SLM). An SLM may be an array of individually addressable optical elements (e.g., mirrors) representing pixels of an image. To this end, an SLM is similar to a DMD array. The SLM directs a series of pixel-reflected light beams to a single-cell photosensor. A control circuit switches the optical pixel elements between ON and OFF positions to either direct a light beam to the photosensor (ON position) or away from the photosensor (OFF position). The photosensor detects each pixel-reflected light beam at a time and generates an image signal in response. As an enhancement, a plurality of photosensors can be used wherein each photosensor is assigned to each optical pixel element. This allows multiple light beams from multiple optical pixel elements to be detected and processed in parallel. The image signal is then digitized by an ADC before being stored in memory. Like the digital camera of patent ""736, the digital camera of patent ""555 also has a fixed resolution because of the fixed number of the optical pixel elements that can only either be turned ON or OFF. In addition, like the digital camera of patent ""736, the digital camera size is controlled by the level of miniaturization of the SLM which may greatly affect the cost.
Thus, a need exists for a high-resolution digital image capturing apparatus with variable resolution capability that is inexpensive, miniaturized, and power efficient.
Accordingly, the present invention provides a high-resolution digital image capturing apparatus with variable resolution capability that is inexpensive, miniaturized, and power efficient.
The present invention meets the above need with a digital image capturing apparatus comprising an imager circuit, a motion control mechanism, memory, and a processor. In one embodiment of the present invention, the imager circuit is used to capture image pixel data of an image object via an optical lens. The motion control mechanism, which is coupled to the imager circuit, is used to incrementally reposition the imager circuit relative to the image object. The repositioning allows the imager circuit to capture different frames of image pixel data of the image object at different positions. In other words, the repositioning allows existing photosensitive elements in the imager circuit to be reused in dead zones (i.e., gap between two adjacent photosensitive elements which has the equivalent benefits as having additional photosensitive elements. Memory is coupled to the imager circuit and stores the frames of captured image pixel data of the image object. The processor is coupled to the memory, the imager circuit, and the motion control mechanism. The processor combines and processes the frames of captured image pixel data into one image thereby improving the object image resolution.
In an alternate embodiment, the motion control mechanism is used to incrementally displace reflected light beams from the image object relative to the imager circuit to allow the imager circuit to capture different frames of image pixel data of the image object at different positions. Essentially, displacing the reflected light beams relative to the imager circuit has the same effects as moving the imager circuit relative to the object.
For either embodiments, the total number of captured frames may be greatly reduced without any significant loss of resolution by utilizing the concept of fractal geometry. By reducing the total number of captured frames, less time is required for capturing and processing thereby improving the system""s operating time.
All the features and advantages of the present invention will become apparent from the following detailed description of its preferred embodiment whose description should be taken in conjunction with the accompanying drawings.